linux C++通过ntp协议获取网络时间

转自：http://blog.csdn.net/ccjjyy/article/details/42871993

#include <stdio.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <netdb.h>

#include <time.h>

#include <string.h>

#include <iostream>

void ntpdate();

int main() {

ntpdate();

return 0;

}

void ntpdate() {

//char *hostname=(char *)"163.117.202.33";

//char *hostname=(char *)"pool.ntp.br";

char *hostname=(char *)"200.20.186.76";

int portno=123; //NTP is port 123

int maxlen=1024; //check our buffers

int i; // misc var i

unsigned char msg[48]={010,0,0,0,0,0,0,0,0}; // the packet we send

unsigned long buf[maxlen]; // the buffer we get back

//struct in_addr ipaddr; //

struct protoent *proto; //

struct sockaddr_in server_addr;

int s; // socket

long tmit; // the time -- This is a time_t sort of

//use Socket;

//

//#we use the system call to open a UDP socket

//socket(SOCKET, PF_INET, SOCK_DGRAM, getprotobyname("udp")) or die "socket: $!";

proto=getprotobyname("udp");

s=socket(PF_INET, SOCK_DGRAM, proto->p_proto);

perror("socket");

//

//#convert hostname to ipaddress if needed

//$ipaddr = inet_aton($HOSTNAME);

memset( &server_addr, 0, sizeof( server_addr ));

server_addr.sin_family=AF_INET;

server_addr.sin_addr.s_addr = inet_addr(hostname);

//argv[1] );

//i = inet_aton(hostname,&server_addr.sin_addr);

server_addr.sin_port=htons(portno);

//printf("ipaddr (in hex): %x\n",server_addr.sin_addr);

/*

* build a message. Our message is all zeros except for a one in the

* protocol version field

* msg[] in binary is 00 001 000 00000000

* it should be a total of 48 bytes long

*/

// send the data

printf("sending data..\n");

i=sendto(s,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,sizeof(server_addr));

perror("sendto");

// get the data back

struct sockaddr saddr;

socklen_t saddr_l = sizeof (saddr);

i=recvfrom(s,buf,48,0,&saddr,&saddr_l);

perror("recvfr:");

//We get 12 long words back in Network order

/*

for(i=0;i<12;i++) {

//printf("%d\t%-8x\n",i,ntohl(buf[i]));

long tmit2=ntohl((time_t)buf[i]);

std::cout << "Round number " << i << " time is " << ctime(&tmit2) << std::endl;

}

*/

/*

* The high word of transmit time is the 10th word we get back

* tmit is the time in seconds not accounting for network delays which

* should be way less than a second if this is a local NTP server

*/

//tmit=ntohl((time_t)buf[10]); //# get transmit time

tmit=ntohl((time_t)buf[4]); //# get transmit time

//printf("tmit=%d\n",tmit);

/*

* Convert time to unix standard time NTP is number of seconds since 0000

* UT on 1 January 1900 unix time is seconds since 0000 UT on 1 January

* 1970 There has been a trend to add a 2 leap seconds every 3 years.

* Leap seconds are only an issue the last second of the month in June and

* December if you don't try to set the clock then it can be ignored but

* this is importaint to people who coordinate times with GPS clock sources.

*/

//tmit-= 2208988800U;
tmit-= 2209017600U;

//printf("tmit=%d\n",tmit);

/* use unix library function to show me the local time (it takes care

* of timezone issues for both north and south of the equator and places

* that do Summer time/ Daylight savings time.

*/

//#compare to system time

//printf("Time: %s",ctime(&tmit));

std::cout << "time is " << ctime(&tmit) << std::endl;

i=time(0);

//printf("%d-%d=%d\n",i,tmit,i-tmit);

//printf("System time is %d seconds off\n",(i-tmit));

std::cout << "System time is " << (i-tmit) << " seconds off" << std::endl;

}